The present invention relates to a core drill for forming a hole in the form of a cylinder in materials like stones, base rocks or concrete structure and particularly to a core drill wherein initial frictional resistance for segment tips is reduced at the time of settling on an article to be processed for a hole to stabilize the initial work and helical groove is formed on the core body to facilitate the discharge of cut chips or wet sludge for improving cooling performance and for improving cutting performance through reduced rotational resistance.
Generally, a core drill comprises a cylindrical core body with a finite diameter and length and segment tips of diamond fixed at the bottom surface of a core body for drilling an article, wherein the core drill is connectable to a drilling machine through screwed fixing part formed on the top of the core body.
Thus, the core drill is connected to a core drill machine and actuated to form a hole in a stone, concrete structure or base rock by cutting or drilling with the segment tips.
As prior art literatures, there are Korean utility model publication No. 1996-0006713(05.08.1996) to the present applicant and Korean unexamined U.M. publication No. 2000-0015639(05.08.2000) to S. H. Kang.
In the core drills according to the above-described prior disclosures, the cutting segment tips have flat thickness surface with a large surface area and experience a large frictional resistance in settling on an article and so tend to slip away, making initial settling difficult.
For example, when a worker tries to make a hole on the bottom or side wall of a concrete structure, he sets the core drilling machine in vertical or horizontal direction, causes the segment tips mounted on the core drill to make a close contact with the surface of concrete through application of force in the corresponding direction and then starts to perform drilling by actuating the core drilling machine. However, during some initial period he has to make several tries for settling the drill stably on the concrete because the segment tips easily slip off due to the small concentrated pressure from the large contacting surface between the concrete and segment tips, until he finally succeeds in drilling.
The above-described settling gets more difficult as the specification or the diameter of a core body increases, and on the other hand if the surface of the article to be processed is more slippery or its hardness is high, the settling gets more difficult. The settling or room making requires so much time in drilling operation that it influences the working efficiency and so the productivity.
On the other hand, the prior art core drills are each formed with one or more rows of helical grooves on the inside and outside or the outside only to guide and discharge the cut powder or sludge generated as the cutting segment tips perform drilling work.
Here, the problem is with the location of the starting positions of the helical grooves, because the starting points are positioned intermediately between the neighboring segment tips fixed on the bottom of a core body in ignorance of the cutting of a material taking place at the segment tips.
In other words, although connecting paths for conveying the cut chips or sludge produced at segment tips to the helical grooves need to be provided in order that the cut powder or sludge may be discharged along the helical grooves when a core drill is in operation of cutting an article with segment tips, the starting points of the helical grooves are positioned at a distance from segment tips, with no connecting paths provided. Thus, the cut scraps stay in motion between the segment tips for some while and only a part of them reaches the helical grooves to be discharged through the grooves, whereby smooth discharge of scraps is not realized. As a result, the remaining cut scraps may move un-oriented inwardly of the core body or outside the circumference of the core body and can come into contact with the scraps newly produced to increase the friction on the core body, so that the rotation of the core body is hindered and the cutting performance of the core drill is that much deteriorated.
The present invention was created to resolve the problems with the conventional art and so the object of the invention is to provide a core drill by which initial drilling workability is improved through reduced frictional resistance on the segment tips, when they are settled on the surface of an article to start cutting operation, and in which cut scraps or sludge produced by the segment tips are smoothly discharged through the helical grooves formed on the core body so as to reduce the friction between the core body and the cut scraps or sludge, whereby both the cooling and cutting performance of a core drill are improved.
The above object is achieved according to the invention by a core drill with a cylindrical core body with a predetermined diameter and length and with plural cutting segments provided on the lower part of a core body at a finite interval, wherein the cutting thickness surface of the cutting segment consists of inclined sharp thickness portion for decreased frictional resistance with an article to be processed.
Preferably, said sharp thickness portion is formed by inclination from the outside arc, the inside arc or from both the outside and inside arc of a segment tip.
According to another feature of the invention, the segment tips each including the sharp thickness portion from outside arc are arranged in one direction on a core body, or the segment tips each including the sharp thickness portion from outside arc and the segment tips each including the sharp thickness portion from inside arc are arranged alternately on a core body.
The object is also achieved according to another aspect of the invention by a core drill with a cylindrical core body with a predetermined diameter and length and with plural cutting segments provided on the lower part of a core body at a finite interval, wherein out of one or more rows of helical grooves formed from the bottom of a core body up toward the top at a finite interval on the surface of the core body, at least one row of helical groove has its starting point at a segment tip mounted on the under side of the core body.
Further preferably, one or more rows of helical grooves formed from the bottom of a core body up toward the top at a finite interval on the surface of the core body have their starting points at the segment tips mounted on the under side of the core body.
Still further, the inclination angle of said helical grooves preferably lies in the range between 1xc2x0 and 90xc2x0 relative to the horizontal.
Moreover, preferably the inclination angle of the helical grooves formed on the core body is the same as the inclination angle of the recesses or ridges formed on the arc part of the segment tips mounted on a core body.
According to still other feature of the invention, a plurality of openings in communication with the inside of a core body are formed between neighboring helical grooves on the core body.